It is desirable to limit access to valve controls mounted in an access pipe, for example water valves sunk underground controlling the flow of water from a water main to a business or home. If water to the business or home is unnecessary or if the water bills have not been paid, it is necessary to not only turn off the valve preventing water flow to the user, but also block access to the valve thereby preventing unauthorized access thereto.
A prior valve lock is shown in FIGS. 6-8. Referring now to FIG. 6, there is shown a valve lock 15 mounted at one end of an elongate hollow shaft 17 that has a key housing 19 threadedly engaged at the other end thereof as at 20. This entire structure is receivable in an access pipe leading to a water valve. A shaft 21 extends longitudinally through the key housing 19 and terminates in a key 21 oriented in the hollow pipe 17 for engaging a keyway 22 on an elongate drive shaft 23. The drive shaft 23 operates the valve lock 15 effecting a lock or unlock of same to or from an access pipe 25. The valve lock 15 includes movable plates 26 and fixed plates 27, whereby the movable plates cause locking engagement of the valve lock 15 against the ID surface of the access pipe 25. Guide pins 28 are fixedly mounted in the fixed plates 27 and are received in elongate slots 29 in the upper portion of the movable plates 26 whereby the upper part of the movable plates 26 are guided for radially inward and outward movement on the pins. The movable plates 26 have inclined surfaces 31 at the lower end thereof which are engaged by correspondingly shaped surfaces on a wedge 33 which is movable in response to the rotation of the drive shaft 23 so that the surfaces on the wedge 33 engage the inclined surfaces 31 to drive the movable plates 26 outwardly against the return force of an elastically yieldable rubber ring 34 so that the relatively narrow outer wall of each of the movable plates is forced against the inner wall of the access pipe 25 (FIG. 8). As the key 21 turns the drive shaft 23 the valve lock 15, and more specifically, the radially outwardly facing edge of the movable plates 26, engage the ID surface of the access pipe along a relatively small surface area of the access pipe.
This prior valve lock has the drawback that it does not provide a sufficient surface contact to the ID surface of the access pipe for preventing unintended removal of the valve lock.
Accordingly, it is an object of this invention to provide an improved valve lock that has an increased surface contact to the ID surface of the access pipe.
It is also an object of this invention to apply an outwardly directed force, holding the valve lock in the access pipe, more uniformly distributed around the outer circumference of the valve lock so as to prevent forced manipulation of the valve lock without the assistance of a key.